Field of Invention
The present invention relates to an apparatus for making coal samples, and more particularly to a wind permeation-type dryer capable of scraping material.
Description of Related Arts
Analysis of characteristics of coal involves a process of sampling analysis of the coal. Coal is a non-homogeneous material, such as its particle size and quality characteristics of distribution. The original coal to be sampled for analysis is relatively large (from tens to tens of thousands of tons). The process of obtaining sample that is able to mostly represent the quality and characteristics of all the coal to be sampled is called “sampling”. Presently, there are different methods of sampling such as mechanical sampling, manual sampling, and semi-mechanical sampling. All countries have made compulsory standards respectively that must be followed in sampling.
After samples being sampled following the compulsory standards, the next process is sample preparation, wherein standards of the sample preparation process include gradually reducing the particle size of the samples and gradually decreasing the mass of the samples until they meet the condition required for analysis or testing in the laboratory while under a premise of not destroying the representativeness of the samples. The sample preparation process commonly includes the steps of air-drying, sample reduction, sample division, and sample pulverizing. The process of air-drying is to bring the moisture of the samples near to equilibrium with the atmosphere in the area in which the steps of sample reduction and division to take place so as to facilitate the following steps of sample reduction and sample division. The samples may also be dried by a way of heating, but temperature of the heating should be controlled under 50° C. The process of sample reduction is to reduce the particle size of the samples. The process of sample division is to decrease the mass of the samples while maintaining their representiveness, wherein the remaining samples after the sample division must represent the coal characteristics of the samples before the step of sample division. The step of sample division is the only step in the sample preparation process for decreasing the quantity of the coal samples while the coal samples are not allowed to be lost in quantity in other steps of the sample preparation because any lost of samples in the steps other than sample division (such as coal powder loss, selective loss of waste rock, and etc.) can change the characteristics of the coal samples. Any selective loss of the samples (may not be man-made) is absolutely not allowed during the process of the sample preparation.
With respect to the step of drying the coal samples, there are mainly two methods to reduce a moisture of the coal samples presently:
(1) A method of drying by natural air: This method doesn't change the quality characteristics of the coal. However, the efficiency is too low, the cost time is too much (generally 24-48 hours), and the space occupied is relatively too big.
(2) A method of drying by hot air and a large oven: This method uses a heating lamp with high power or an oven with high power to dry the coal samples and reduce the moisture of the coal samples. Since this method doesn't analyze the two processes of mass transfer during the process of reducing the moisture of the samples, the evaporation only happens on the surface of materials and the moisture in inner layers of the materials can hardly be evaporated out. If the air on the surface of the materials reaches saturation of water absorption, the air on the surface of the materials will no longer absorb into moisture any more. If the air on the surface of the materials is not to be sucked off or exchanged timely, the evaporation will stop essentially. Thus, this method is not efficient as it cannot quickly reduce the moisture of the materials and cost too much time. Since a common fan is applied on the oven, the rate of air exchanging and its efficiency are very low, which lead to the air in the oven approach to the point of water saturation. Thus, the efficiency of using the oven to dry the materials with rich moisture is very poor.
Another method to reduce moisture is based on ventilation, wherein the method uses hot air to blow through the materials to reduce the moisture of the materials. However, conventional equipment always have the following problems:
(1) A low level automation, non-homogeneity drying caused by a disorderly piling of the coal samples, low efficiency of reducing the moisture of the coal samples, and high labor intensity of operators.
(2) Prolonging the process of reducing the moisture of the samples for the coal samples piled on the bottom layer, which may destroy the coal samples piled on the outer layer, so as to decrease the quality and accuracy of the coal samples.
(3) Prolonging the process of reducing the moisture of the samples, which causes a high-energy consumption of the equipment and influences the service life of the equipment.